Harsh S's in Voice Track

Every pronounced S in one of my audio voice overs is really intense and painful to listen to - what is the best method for reducing this? I have access to both Adobe Soundbooth and Final Cut Pro Suite.

True but it's not a solution to the problem. The problem is the narrators enunciation and speech patterns, both of which can be corrected by a speech therapist or by having the narrator listen to the track and have them work on correcting the issue themselves.

You said ONE of your voice tracks. If only one of the tracks is a problem, the problem may not be excessive sibilance. There may be a technical reason.

Sibilance is created when we say words with S, C, CH and Z sounds. Some people over emphasize these sounds by unintentional placement of the tongue on the hard palate behind the upper front teeth.

Eric is correct; a pop filter will not be effective here. Although thick foam filters may reduce all high frequencies to some degree, they are designed to be transparent. It's better to fix the problem at the source. I had a client with this problem and 4-6 visits to a speech therapist solved it.

If the problem is in a recording you can't redo and the problem is excessive sibilance, you may be able to reduce the problem by using a de-esser plugin. If that doesn't work you can manually fix each problem by carefully shortening and/or lowering the level of the offending SZZZ sounds.

Zoom in on the waveform. The offending sound will be lower in level, but very dense. split the file to isolate the spot, select the spot and try reducing the gain by 6-8 dB. I have found that up to 12 dB may be required before the problem goes away.